1. Field of the Invention
The present invention relates to a thermal head drive apparatus used in a printer, a copying machine. etc.
2. Description of the Related Art
In a general thermal head drive apparatus, a thermal head has a plurality of heating resistors arranged in a line and is driven by using image data. In such a thermal head drive apparatus, image data of an object picture element are corrected to correct an influence of the object picture element on density by heat-accumulating states of the heating resistors. Such a structure is shown in Japanese Patent Application Laying Open (KOKAI) No. 60-131262.
In the above thermal head drive apparatus, the individual heat-accumulating state of the object heating resistor is provided by giving weights in accordance with the positions of the respective picture elements to the image data of the respective picture elements around the object picture element and performing an additional operation with respect to the weighted data. Accordingly, when the image data are binary data, it is possible to calculate the heat-accumulating states of the heating resistors since an information amount of the image data of the picture elements is small. However, when the image data are multivalued data and an image at multiple gradations is printed, it is necessary to calculate the heat-accumulating states of the heating resistors from the image data of the picture elements arranged before a predetermined line in addition to the image data of the picture elements since the image data arranged before the predetermined line give an influence to the density of the object picture element. Accordingly, the information amount becomes very large and the apparatus is large-sized so that it is almost impossible to practice the drive apparatus.